Climate change report: California to see 77 percent more...

1of3A helicopter drops water to protect a home at the Holy Fire in Lake Elsinore, southeast of Los Angeles. A new state report projects that the amount of land burned annually by wildfire will rise 77 percent by the end of the century.Photo: ROBYN BECK / AFP/Getty Images

2of3Fires like the one that destroyed the Mary Estates subdivision in Redding last month will likely increase by 50 percent in California by the end of the century, according to a state report.Photo: Gabrielle Lurie / The Chronicle

3of3Alex Schenck tries to save his Clearlake Oaks home on Aug. 4 from the Ranch Fire, the largest in state history.Photo: Noah Berger / AFP / Getty Images

This year’s wildfire season is not the worst that California will see.

The number of large fires across the state will likely increase by 50 percent by the end of the century while the amount of land that burns annually will rise 77 percent, according to a new, far-reaching state report that seeks to document the impacts of climate change.

And the problems don’t end here. California’s Fourth Climate Change Assessment, released Monday by the governor’s office with other state agencies, portrays a multiheaded threat that promises more wildfires at the same time that higher seas overrun beaches, less water fills state reservoirs and drier weather shrivels Central Valley crops.

“It’s all of these things happening in combination. That’s the scary part,” said Bob Weisenmiller, chair of the California Energy Commission, one of the agencies that helped compile the report. “There were times when people thought we had the rest of the century to act on climate change. But climate change is upon us now, and we have to act right now.”

The report draws on previously published studies about California’s future and includes new research from dozens of scientists, all of whom underscore the state’s numerous vulnerabilities in coming decades, even amid efforts to fight and adapt to climate change. Policies of the Trump administration, which has de-emphasized the reduction of planet-warming carbon dioxide, have only exacerbated matters.

“In California, facts and science still matter,” said Gov. Jerry Brown in a prepared statement. “These findings are profoundly serious and will continue to guide us as we confront the apocalyptic threat of irreversible climate change.”

The deadly Carr Fire in Redding and the record-big Mendocino Complex near Clear Lake are among the blazes that have cumulatively charred 1.1 million acres in California this year — about as much land as the state of Delaware. It’s more than three times the five-year average.

“We’re on a trajectory of a lot more area burned than even what we’ve been projecting,” Westerling said.

Westerling’s new projections suggest fires of at least 25,000 acres will occur 50 percent more often by 2100 if greenhouse gas emissions continue at their current rate. Those projections are based on models that simulate higher temperatures and more variable rainfall, meaning longer dry spells.

While Westerling expects burned acreage to rise by the end of the century by 77 percent of the current average, some years will see nearly three times as much land go up in smoke, according to his research.

This dire forecast can be tempered, he said, if state and federal land managers commit to more aggressive forest management, including precision thinning of woodlands and setting controlled fires. These strategies have long faced resistance, however, for reasons ranging from fear of damaging forests to complaints about smoke from prescribed burns.

Westerling’s research suggests if 30 percent of the Sierra Nevada was appropriately managed, the amount of land that burns could drop nearly a third.

“We can totally do it,” Westerling said. “It’s all about political will.”

The state report warns that if wildfires aren’t mitigated, the impacts will cascade beyond the fire lines. Smoke will drive more respiratory illness, the power grid will lose more lines and equipment to flames, and even the cost of homeownership will rise. The price of wildfire insurance, for example, is projected to increase 18 percent by 2055 as fires become more damaging.

California’s water supply also faces risk of disruption, according to the report, threatening a $46 billion agricultural economy and portending increased water restrictions in cities and towns.

The basic problem is snow. As temperatures warm, the Sierra snowpack that provides much of the state’s water will melt earlier and become gradually more limited. By 2100, the snowmelt will be as much as 80 percent scarcer, the report said. That will mean less water flows into reservoirs in summer when demand is greatest.

“Our system was built for a different climate,” said John Andrew, assistant deputy director for the California Department of Water Resources, which oversees the State Water Project and its nearly two dozen reservoirs.

While issues with water have been identified in older studies, the report provides new estimates for how much won’t be available for export through the Sacramento-San Joaquin River Delta, the state’s water-supply hub: about 10 percent less will flow by 2060.

“It’s not the end of the world,” Andrew said, “but 10 percent in a system that’s already strained is something to pay attention to.”

In the future, Californians will have to rely less for their water on big reservoirs managed by the state and federal governments, the report advises, and more on local initiatives, from desalination plants to water recycling to conservation.

The dip in water supplies will come as the demand for water on agricultural lands will rise as a result of increased evaporation, by 8 percent by midcentury, according to the report. Nearly 70 percent of California’s winemaking area is thought to be vulnerable.

The Climate Change Assessment also provides new projections for sea-level rise. Between 31 and 67 percent of Southern California beaches may wash away by the end of the century without large-scale intervention, according to the report.

The authors of the new assessment hope the report serves as a call for action as well as provides guidance on where the most immediate threats lie and ways to address them. The document updates scientific projections made in the prior assessment, in 2012, and contains new sections that pinpoint the problems of specific regions.

“The basic message is that changes are happening fast, and they’re not good changes,” said Weisenmiller, with the Energy Commission. “We need to rise to the challenge.”

Kurtis Alexander is a general assignment reporter for The San Francisco Chronicle, frequently writing about water, wildfire, climate and the American West. His recent work has focused on the impacts of drought, the widening rural-urban divide and state and federal environmental policy.

Before joining the Chronicle, Alexander worked as a freelance writer and as a staff reporter for several media organizations, including The Fresno Bee and Bay Area News Group, writing about government, politics and the environment.